One-piece manufacturing process

ABSTRACT

A method of making a turbomachine part, wherein the method can include machining a blank into a base having blades extending therefrom, the blades defining a channel therebetween. The method can also include forming a bridge constructed from refractory material in the channel between the blades, and forming a cover on the tops of the blades and over the channel, such that the base, the blades, and the cover form a single substantially homogenous turbomachine part once the bridge is removed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 13/442,068, which was filed on Apr. 9, 2012, which is acontinuation-in-part of U.S. patent application Ser. No. 12,917,750,which was filed Nov. 2, 2010, which issued as U.S. Pat. No. 8,151,862and claims priority to U.S. Provisional Patent Application Ser. No.61/258,524, which was filed Nov. 5, 2009, the disclosures of which areincorporated herein by reference in their entirety to the extentconsistent with the present application.

BACKGROUND

Various methods of fabricating turbomachinery parts, including impellerblades, diaphragms, and guide vanes, are known. Typically, such partsare assembled from smaller forged and machined parts. The smaller partsare machined to tight tolerances and then fixed together such as bywelding, brazing, or e-brazing.

However, such machining and fixing processes are time-intensive andcostly, and typically yield turbomachinery parts that are comprised ofmultiple distinct pieces. Having these multiple distinct piecesnecessitates joints where stress can be concentrated, which can lead todeformation or even failure, thereby reducing the effective life of theturbomachinery part.

One way of overcoming this is by casting the part as a whole. However,casting is typically not useful in parts requiring tight tolerances.Further, the finished casting surface can be rough compared to machinedsurfaces. In parts that manipulate high velocity and/or pressure fluid,the roughness of the surface and the tolerances are critical toefficiency, such that casting is not typically useful for manyturbomachine parts. What is needed, therefore, is a method of makingturbomachine parts that does not suffer from the stress,time-consumption, and/or other drawbacks of the multiple-pieceassemblies, or the inaccuracy and/or other drawbacks of conventionalcasting methods.

SUMMARY

Embodiments of the disclosure provide a method of making a one-piecepart, the method including machining a blank into a base and first andsecond appendages extending from the base, the first and secondappendages each having a side, the side of each of the first and secondappendages together defining a channel therebetween; forming a bridge inthe channel; forming a cover on the first and second appendages suchthat the base, the first and second appendages, and the cover form asingle, unitary structure; and removing the bridge.

Embodiments of the disclosure further provide a method of making aturbomachine part, wherein the method includes machining a blank into abase having first and second blades extending therefrom, the first andsecond blades each having a side, the side of each of the first andsecond blades together defining a channel therebetween. The methodfurther includes forming a bridge in the channel between the first andsecond blades, forming a cover on first and second tops of the first andsecond blades, respectively, and over the channel, such that the base,the first and second blades, and the cover form a single substantiallyhomogenous structure, and then removing the bridge.

Embodiments of the disclosure further provide a method of making aturbomachine part, wherein the method includes machining a blank into abase and first and second blades extending from the base, the first andsecond blades each having a top and a side, wherein the side of each ofthe first and second blades and the base together define a channelbetween the first and second blades. The method may further includeforming a bridge across the channel using a ceramic slurry, forming acover on the first and second blades and the bridge such that the base,the first and second blades, and the cover form a single substantiallyhomogenous structure, and then removing the bridge.

Embodiments of the disclosure further provide a method of making animpeller for a turbomachine, wherein the method includes machining ablank into a base and first and second blades extending from the base,the first and second blades each having a top and a side, wherein theside of each of the first and second blades and the base define achannel between the first and second blades, forming a bridge across thechannel using a ceramic slurry, forming a cover on the first and secondblades and the bridge using laser cladding, such that the base, thefirst and second blades, and the cover form a single substantiallyhomogenous structure, and then removing the bridge.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying Figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale. In fact, the dimensions of the variousfeatures may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a flow chart of an exemplary method of making aone-piece turbomachine part, according to one or more aspects of thedisclosure.

FIG. 2 illustrates a side view of a blank, according to one or moreaspects of the disclosure.

FIG. 3 illustrates an enlarged side view of the blank of FIG. 2, whichhas been machined into a base and blades, according to one or moreaspects of the disclosure.

FIG. 4 illustrates a flow chart of an exemplary method of forming thebridges and the cover, according to one or more aspects of thedisclosure.

FIG. 5 illustrates a side sectional view of an exemplary embodiment ofthe base and the blades and dam with a core formed between the blades,according to one or more aspects of the disclosure.

FIG. 6 illustrates an enlarged side sectional view of a portion of FIG.5, according to one or more aspects of the disclosure.

FIG. 7 illustrates an enlarged side sectional view of a portion of FIG.6, according to one or more aspects of the disclosure.

FIG. 8 illustrates a side view of the base and the blades with a coverhomogeneously formed therewith, according to one or more aspects of thedisclosure.

FIG. 9 illustrates a side view of an exemplary embodiment of theturbomachine part, according to one or more aspects of the disclosure.

FIG. 10 illustrates a simplified side sectional view of a base andblades undergoing a laser deposition process, according to one or moreaspects of the disclosure.

FIG. 11 illustrates a side view of an exemplary cover formed by thelaser deposition process, according to one or more aspects of thedisclosure.

FIG. 12 illustrates a flow chart of another exemplary method of formingthe bridge and the cover, according to one or more aspects of thedisclosure.

FIG. 13 illustrates a side sectional view of an exemplary embodiment ofthe base, the blades, a cast fitted thereon, and a shell formedtherearound, according to one or more aspects of the disclosure.

FIG. 14 illustrates the sectional view of FIG. 13, with the wax patternremoved and a molten material poured into the shell, according to one ormore aspects of the disclosure.

FIG. 15 illustrates a side sectional view of an exemplary disk-shapedcast fitted over the blades in preparation for the laser depositionprocess, according to one or more aspects of the disclosure.

FIG. 16 illustrates a side sectional view of an exemplary embodiment ofthe cover formed by the laser deposition process using the shell,according to one or more aspects of the disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure describes severalexemplary embodiments for implementing different features, structures,or functions of the invention. Exemplary embodiments of pieces,arrangements, methods, and configurations are described below tosimplify the present disclosure, however, these exemplary embodimentsare provided merely as examples and are not intended to limit the scopeof the invention. Additionally, the present disclosure may repeatreference numerals and/or letters in the various exemplary embodimentsand across the Figures provided herein. This repetition is for thepurpose of simplicity and clarity and does not in itself dictate arelationship between the various exemplary embodiments and/orconfigurations discussed in the various Figures. Moreover, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed interposing the first and secondfeatures, such that the first and second features may not be in directcontact. Similarly, where a method or sequence is described, thedescribed method is not intended to be limited to only those stepsdescribed herein. Rather, additional steps or processes may be added tothe method at any point during the method sequence without departingfrom the scope of the invention. Finally, the exemplary embodimentspresented below may be combined in any combination of ways, i.e., anyelement or method step from one exemplary embodiment may be used in anyother exemplary embodiment, without departing from the scope of thedisclosure.

Additionally, certain terms are used throughout the followingdescription and claims to refer to particular pieces. As one skilled inthe art will appreciate, various entities may refer to the same piece bydifferent names, and as such, the naming convention for the elementsdescribed herein is not intended to limit the scope of the invention,unless otherwise specifically defined herein. Further, the namingconvention used herein is not intended to distinguish between piecesthat differ in name but not function. Further, in the followingdiscussion and in the claims, the terms “including” and “comprising” areused in an open-ended fashion, and thus should be interpreted to mean“including, but not limited to.” All numerical values in this disclosuremay be exact or approximate values unless otherwise specifically stated,and as such each numerical value stated in the description should beinterpreted to be “about” the recited value. Accordingly, variousembodiments of the disclosure may deviate from the numbers, values, andranges disclosed herein without departing from the intended scope.Furthermore, as it is used in the claims or specification, the term “or”is intended to encompass both exclusive and inclusive cases, i.e., “A orB” is intended to be synonymous with “at least one of A and B,” unlessotherwise expressly specified herein.

FIG. 1 illustrates a flow chart of an exemplary method 100 of forming aturbomachine part, where the part may be an impeller. The method 100begins at 102 where a blank, which is generally a metal or metal-alloystock material, is machined into a base with a plurality of appendagessuch as, for example, a plurality of blades, extending therefrom. Theexemplary method 100 continues to 104, where a bridge is formed betweenthe blades, and then at 106 a cover is formed over the blades, such thatthe cover, the base, and the blades preferably form a singlesubstantially homogenous structure. Finally, at 108 the bridge isremoved and the part is completed. Removal of the bridge can includeshaking, vibrating, or pushing the bridge out of from between the bladesto yield only the remaining metal of the part itself. As the term isused herein, “single homogeneous structure” is generally defined to meanthat the microstructure of the part is the same throughout the part,such that there is no significant discernable difference in themicrostructure where the cover and the base come together. For example,the single homogeneous structure may be nearly indistinguishable from astructure that is originally cast as a single part. In variousembodiments, instead of forming a single, unitary structure that issubstantially homogenous at 106, a single, unitary structure that is nothomogenous is formed at 106, but is further processed through heattreatment and/or isostatic pressing to form a single homogeneousstructure. Each of the respective processes of method 100 will bedescribed in turn, with reference to exemplary embodiments of thepieces, which are depicted in the figures.

FIG. 2, with continuing reference to FIG. 1, illustrates a side view ofan exemplary embodiment of a blank 10. The blank 10 is generallymachined to include a base 12 and appendages such as, for example,blades 13, extending therefrom. Preferably the blank 10 can include anynumber of blades 13, for example, 6, 8, 12, or more blades 13 may beincluded as desired. As will be readily appreciated, the blades 13 maybe curved and may extend radially from a middle terminus (not shown) toan outside diameter (not shown) of the base 12, but in other embodimentscan extend straight radially out from the middle terminus. Accordingly,the blank 10 can be shaped generally as an impeller lacking a cover, butin other exemplary embodiments, the blank 10 can have the general shapeof any turbomachine part, such as a guide vane assembly, a diaphragm, orthe like. The blank 10 can be fabricated in any way, for example, theblank 10 can begin as a solid disk or block of forged metal, which canbe initially milled or machined to form the base 12 having the blades 13extending therefrom. In another embodiment, the blank 10 can be cast,for example, by investment or injection casting, or the like. Inembodiments where the blank 10 is cast, the resulting cast base 10 maystill be machined to provide more accurate tolerances in the base 10. Invarious other embodiments, the blank 10 can be formed by laserdeposition or other known processes of forming a turbomachine part. Invarious embodiments, instead of, or in addition to, the blades 13, theblank 10 may include other types of appendages extending from the base12 such as, for example, protrusions, walls, protuberances, ribs,supports, beams, members, and/or any combination thereof.

FIG. 3, with continuing reference to FIG. 1, illustrates an enlargedside view of a portion of the base 12 and first and second blades 14, 16after the milling process of 102 is performed on the blank 10. Themilling process can remove a portion of the first and second blades 14,16 such that the first and second blades 14, 16 take desired dimensionswithin a desired dimensional tolerance. For example, the dashed lineshows an exemplary embodiment of the blank 10 before the millingprocess, while the solid lines indicate the blank 10 after the millingprocess of 102. The milling process can be any suitable milling process,such as 5-axis computer-controlled milling, or other machining processesused in the art. The first and second blades 14, 16 have sides 20, 22,respectively, which define an open channel 23 therebetween. In anexemplary embodiment, channel 23 can be an impeller channel for acentrifugal compressor or a turbine, but in other embodiments can be anytype of turbomachine impeller channel.

The desired dimensions of the first and second blades 14, 16 cangenerally include a height H_(B) of the blades 14, 16, defined from theintersection of the bottom 28 and the base 12 to the edge of the top 24.In an exemplary embodiment, the height H_(B) can be from about 0.5inches to about 5 inches, or can be about 1 inch, but it will beappreciated that substantially any height H_(B) may be created asdesired. The desired dimensions can also include a width W of thechannel 23 at the radial outside of the base 12. In various exemplaryembodiments, the width W may be from about 1 inch to about 10 inches, ormay be about 3 inches, but in various exemplary embodiments can be anywidth W depending on the application. The dimensions can also include athickness T of the first and second blades 14, 16, which can be fromabout 1/16 of an inch to about 5/16 of an inch, or can be about 3/16 ofan inch, or can be any other thickness T suitable for a particularapplication. Furthermore, the dimensions H_(B), W, and T can change, forexample, they may shrink, along the course of the blades 14, 16 as theydraw nearer the middle terminus (not shown).

The milling process can also define (i.e., cut) flared or filleted bladetops 24 into the first and second blades 14, 16. The flaring of the tops24 can increase the top 24 surface area of the first and second blades14, 16. Similarly, the milling process can also cut flared bottoms 28such that the cross-section of the first and second blades 14, 16increases proximal the base 12. The flaring of the bottoms 28 canprovide increased strength for the integral formation of the base 12 andthe first and second blades 14, 16.

With continuing reference to FIG. 1, FIG. 4 illustrates a flow chart ofan exemplary embodiment of forming a bridge, as represented by box 104in FIG. 4. Additionally, box 106 in FIG. 4 illustrates the process offorming the cover over the base. The process of forming the bridge maybegin at 402, where the channels 23 are filled with a refractorymaterial to form a core 32, as shown in FIG. 5. The core 32 can providebridges 33 across each channel 23, where the bridges 33 aresubstantially planar and connect adjacent blade tops 24. The refractorymaterial forming core 32 and bridges 33 may be a resin-coated sand, aceramic molding material, or any suitable cast filling material. Theprocess of forming the bridge may also include heating the base, asshown at 404. The base may be heated to any suitable temperature to curethe refractory material of the core 32. In one embodiment the base 12may be heated to between about 200° F. to about 500° F.

Excess portions (not shown) of the core 32 can be, for example, struckoff with a straight-edged tool prior to or after curing, such that thecore 32 is leveled with the tops 24 of the blades 13. As such, in anexemplary embodiment, the core 32 leaves the blade tops 24 uncovered orexposed. The core 32 can also be smoothed to promote a smooth castingsurface.

Once the channel is filled with the appropriate casting material, themethod may continue to either 406 or 414 to form the cover on or overthe base 12. Continuing to 406 involves using a casting process to formthe cover, whereas continuing to 414 uses a laser deposition process toform the cover.

When the cover is formed by a casting process, the method begins at 406where the outside diameter of the base 406 is surrounded by a ceramicring dam 34, as depicted in FIG. 5. The dam 34 can have a height HD thatis greater than the height H_(B) (FIG. 3) of the blades 13, and further,the dam 34 will generally have a height that is greater than the sum ofthe blade height H_(B) plus the height of the cover element being formedon top of the base 10. As such the dam 34 can define a bounded region 36encircled therein, the bottom of the bounded region 36 being defined bythe tops 24 of the blades 13 and the core 32, and the top of the boundedregion 36 being defined by the top of the cover being formed thereon, asfurther described herein. As shown in FIGS. 5 and 6 but equallyapplicable to other embodiments shown herein, a layer of carbon 35 maybe positioned on one or more sides of the core 32, as will be describedin greater detail below. In other embodiments, the layer of carbon 35may be omitted.

Once the dam 34 is positioned, a molten material, such as molten metal(e.g., steel or other alloy desired to form the part), can be poured,injected, or otherwise applied into the bounded region 36, as shown at408 in the method of FIG. 4 and as depicted in FIG. 6. In at least oneembodiment, the molten material 38 can be made of the same material asthe base 12 and the blades 13 and can cover the exposed tops 24 and thecore 32. The molten material 38 can be superheated to a temperature inexcess of the temperature required to melt the material and thus formthe molten material 38. Further, the blades 13 can be pre-heated to atemperature slightly below the melting temperature thereof, such thatthe amount of heat flux required to raise the blades 13 to the meltingtemperature thereof is reduced. As such, the molten material 38 can melta portion of the tops 24 and coalesce thereto when the molten material38 is poured into the bounded region 36.

FIG. 7 shows an enlarged view of the dashed box in FIG. 6, andillustrates a portion of each of the tops 24 that can be melted to forma “melt zone” 40, where the molten material 38 and the tops 24 maycoalesce and then cool, as illustrated at 410 of the method of FIG. 4,thereby forming a single substantially homogenous structure. It will beappreciated that the size of the melt zone 40, and the duration of itsexistence, is at least partially dependant on the temperature of themolten material 38 and the temperature to which the blades 13 arepre-heated, along with the size of the surface 24 and the volume of themolten material 38 used in the process. Accordingly, one with skill inthe art will readily understand that these parameters and others can beoptimized to result in the desired coalescing of the first and secondblades 14, 16 and the molten material 38. Regardless of the specifictemperatures and sizes of the parts, embodiments of this disclosurecontemplate that the interface or joint between the blades 13 and thecover material 38 will be substantially homogenous and will contain asubstantially consistent crystalline structure across the interfacebetween the two portions of the final part.

FIG. 8 illustrates the side view of FIG. 6 once the molten material 38and the blades 13 have cooled into a solid unitary piece or part, as at410 in the method of FIG. 4. Upon cooling, the molten material 38 mayharden into a disk 42, and the dam 34 can subsequently be removed. Asshown in FIG. 9 and described at 412 in the method of FIG. 4, the coverportion 44 of the disk 42 can then be milled into the desired shape. Thecore material 32 (FIG. 5) can then be removed, for example, by shaking,vibrating, pounding, or pushing the core 32 out, as previously describedat 108 in the method of FIG. 1. As such, the remaining structure is aone-piece or unitary turbomachine part 46, in which the blades 13, thebase 12, and the cover 44 have a substantially homogenous structureacross the joint or interface between the respective elements.

With reference to FIGS. 1-8, to form the desired homogenousmicrostructure, and thereby form a continuous turbomachine part 46, thepre-heat temperature of the blades 13 and the temperature of the moltenmetal are controlled. This ensures proper melting of the blades 13 inthe melt zone 40 (FIG. 7), which enables the desired one-piece structureto form. However, the temperature is also controlled to avoid negativeeffects of over-melting or oxidizing the blades 13, which can inhibitthe precision of the structure, inhibit the formation of a homogenousmicrostructure, or both. In certain embodiments, the turbomachine part46 may be further heat treated or processed, such as by isostaticpressing, to ensure the substantially homogeneous microstructure.

Accordingly, tests indicate that the pre-heat temperature depends on atleast two factors: the thickness T of the blade 13 and the material'stendency to oxidize. Thicker, more massive blades 13 require more energyto melt and therefore a higher pre-heat temperature is desired. However,such increased temperatures may not be practical for metals thatoxidize, for example, titanium. Titanium tends to oxidize above about400° F. compared to, for example, stainless steel alloys, which canbegin to form scale above 700°. In certain embodiments, heating the base12 and blades 13 may be done in a substantially oxygen-free environment,such as an inert gas furnace or a vacuum furnace, to further reduceoxidation.

The optimum temperature of the molten material 38 is also dependent onthe material chosen for the turbomachine part 46 and the thickness ofthe blades 13. Metals with higher melting temperatures require a highertemperature molten material to melt the melt-zone 40 of the blades 13.Similarly, more massive (i.e., thicker) blades 13 require more energy tomelt, and thus a higher temperature for the molten material 38 isrequired.

Continuing with the special case of titanium impellers, which can applyto any metal or alloy that tends to oxidize, the molten titanium itselfmay be subject to oxidation during solidification. Further, the base 12and blades 13 are also heated by their contact and proximity to themolten titanium and thus may also risk oxidation. To avoid oxidationduring solidification of the cover 44 and heating and cooling of thebase 12 and blades 13, the layer of carbon 35 (FIGS. 5 and 6) may beinterposed between the core 32 of refractory material (e.g.,resin-coated sand) and the metal of any of the blades 13, base 12,and/or cover 42 of the turbomachine part 44 prior to and/or duringcasting. This carbon layer 35 inhibits the oxidizing reactions that mayotherwise occur due to the interaction between the hot titanium and therefractory material (i.e., sand).

Referring again to FIG. 4, instead of, or in addition to, pouring themolten material into the area encircled by the dam, a laser depositionprocess, which can also be known as a pulsed laser deposition process ora laser cladding process, can be used to form the cover, as shown at 106in the method of FIG. 4. The laser deposition process can be similar tothe process described in U.S. Pat. No. 5,612,887, the entirety of whichis incorporated herein by reference to the extent it is not inconsistentwith this disclosure. The laser deposition process may include applyinga metal powder and using a laser, for example, a high-intensity UVlaser. As depicted in FIG. 10, the laser can target sequential sectionsof the tops 24 and the bridges 33 such that the laser energizes themetal powder with a plume 49 of laser-generated heat, which may be aplasma in at least one embodiment of the disclosure, thereby melting thepowder. The melted powder can then deposit on the tops 24 and thebridges 33 as a molten metal material, as shown in the method of FIG. 4at 416. The melted powder forms a layer of metal 48 over the tops of thecore material 32, which is continuous and homogenous with the tops 24 ofthe blades 13. The layer of metal 48 typically does not bond to the core32 forming the bridges 33, such that the bridges 33 act as a substrate.The process of depositing the layer of metal 48 can be repeated until,as shown in FIG. 11, the cover 44 results from the repetition of thelaser deposition process. The cover 44 can be formed from this processwithout necessitating additional milling. In various exemplaryembodiments, however, some final milling may be desired.

FIG. 12 illustrates a flow chart of another exemplary embodiment offorming the bridge, as at 104, and at least two exemplary embodiments offorming the cover, as at 106. At 1202, as illustrated in FIG. 13, a castor wax pattern 50 can be fitted on the tops 24 of the blades 13. Thechannel 23 can be open under the wax pattern 50, thereby exposing thesides 20, 22 and the base 12. Ceramic slurry (not shown) can then beapplied to the base 12, the blades 13, and the exterior of the waxpattern 50, such that the slurry can adhere to any exposed portions ofthe base 12, blades 13, and wax pattern 50. The slurry buildup can forma shell 52, as at 1204. The shell 52 can form the bridges 33 betweenadjacent blades 13, and the shell 52 can also form around the outside ofthe wax pattern 50.

The wax pattern 50 can then be removed from inside of the shell 50, asat 1206. In one or more embodiments, the wax pattern 50 can be made ofwax, a polymer, or any suitable material, which can be removed, forexample, by melting and draining, to expose the tops 24 and the bridges33 across the channels 23. In certain embodiments, the shell 52 and base12 can be heated to cure the ceramic slurry and remove the wax patternin a single heating process. In other embodiments, the shell 52 and base12 can be heated to a first temperature to remove the wax pattern 50 andthen heated to a second, higher temperature to cure the ceramic slurry.In an exemplary embodiment, the inside of the shell 52 can have acover-shaped area 53 (FIG. 14) now vacated by the wax pattern 50.

Once the wax pattern 50 is removed, the method may continue to either1208 or 1210 to form the cover on or over the base 10. Continuing to1208 involves using a casting process to form the cover, whereascontinuing to 1210 uses a laser deposition process to form the cover.

When using the casting process, as illustrated in FIG. 14, the moltenmaterial 38 can be poured into the cover-shaped area 53, now defined bythe shell 52, the tops 24, and the bridges 33, as at 1208 of the methodof FIG. 12. As described above with reference to FIG. 7, the moltenmaterial 38 can melt a melt zone 40 of each of the blades 13, such thatthe blades 13 and the molten material 38 blend together or coalesce. Themolten material 38 can be cooled and hardened into the cover 44, asshown in FIG. 9, thereby forming the single homogeneous turbomachinepart 46. However, in other exemplary embodiments, the molten material 38can harden into a disk, similar to the disk 42, shown in and describedabove with reference to FIG. 8, which may subsequently be machined tothe dimensions of the cover 44. The shell 52 and the bridges 33 can beremoved, for example, by vibrating or shaking the turbomachine part 46,as at 108 of FIG. 1.

Referring back to FIG. 12, laser deposition may be used to form thecover, as at 1210. The laser deposition process, as described above withreference to FIG. 10, can be employed by applying, for example blowing,metal powder to the tops 24 and the bridges 33 and melting the metalpowder with a laser. As illustrated in FIG. 15, the wax pattern 50 ofthis embodiment can be similar to the embodiment of the wax pattern 50described above with reference to FIG. 13 and may be shaped, forexample, as a disk. Accordingly, it may not be necessary to form theshell 52 over the top 54 of the wax pattern 50, as the wax pattern 50may not define the final dimensions desired for the cover 44. Further,providing the open top 54 can facilitate access to the tops 24 and thebridges 33 during the laser deposition process. The laser depositionprocess can provide accurate dimensions for the cover 44, as shown inFIG. 16, or, in various other exemplary embodiments, the cover 44 may befinish-milled to the precise dimensions required. The bridges 33 and theshell 52 can then be removed, as at 108 of FIG. 1.

The foregoing has outlined features of several embodiments so that thoseskilled in the art may better understand the detailed description thatfollows. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions andalterations herein without departing from the spirit and scope of thepresent disclosure.

We claim:
 1. A method for fabricating a turbomachine part, comprising: machining a blank into a base having a first appendage and a second appendage extending therefrom, the first appendage and the second appendage defining a channel therebetween; filling the channel with a refractory material to form a bridge between a first top of the first appendage and a second top of the second appendage; forming a cover on the first top and the second top and over the channel such that the base, the first appendage, the second appendage, and the cover form a single substantially homogenous structure; and removing the bridge.
 2. The method of claim 1, further comprising curing the refractory material by heating the base, the first appendage, and the second appendage.
 3. The method of claim 1, further comprising striking off an excess portion of the refractory material such that the bridge is substantially level with the first top and the second top.
 4. The method of claim 1, further comprising depositing a layer of carbon between the refractory material and the cover, between the refractory material and the first appendage, and between the refractory material and the second appendage.
 5. The method of claim 1, wherein machining the blank comprises flaring the first top of the first appendage and the second top of the second appendage.
 6. The method of claim 1, wherein forming the cover further comprises preheating the first appendage and the second appendage to a temperature near a melting temperature thereof.
 7. The method of claim 1, wherein forming the cover comprises disposing a dam around the base such that the dam, the first top, the second top, and the bridge define a bounded region.
 8. The method of claim 7, wherein forming the cover further comprises: pouring a molten metal into the bounded region to melt a portion of the first top and a portion of the second top such that the portion of the first top and the portion of the second top blend with the molten metal; and cooling the molten metal to form the turbomachine part having the single substantially homogenous structure.
 9. A method for fabricating a turbomachine part, comprising: machining a blank into a base having a first vane and a second vane extending from the base, the first vane and the second vane defining a channel therebetween; forming a bridge across the channel and between the first vane and the second vane; preheating the first vane and the second vane to a temperature substantially near a melting temperature thereof; and forming a cover on the first vane, the second vane, and the bridge using a molten metal, the cover being formed such that the base, the first vane, the second vane, and the cover form a single substantially homogenous structure.
 10. The method of claim 9, wherein forming the bridge comprises: filling the channel with a refractory material; curing the refractory material; and striking off excess portions of the refractory material such that the bridge is substantially level with a first top of the first vane and a second top of the second vane.
 11. The method of claim 10, further comprising depositing a layer of carbon between the refractory material and the cover, between the refractory material and the first vane, and between the refractory material and the second vane.
 12. The method of claim 9, wherein machining the blank comprises: flaring a first top of the first vane and a second top of the second vane; and flaring a first bottom of the first vane and a second bottom of the second vane.
 13. The method of claim 9, wherein forming the cover comprises disposing a dam around the base such that the dam, a first top of the first vane, a second top of the second vane, and the bridge define a bounded region.
 14. The method of claim 13, wherein forming the cover further comprises: pouring the molten metal into the bounded region such that a melt zone of the first top, a melt zone of the second top, and the molten metal blend with one another; and cooling the molten metal to form the turbomachine part having the single substantially homogenous structure.
 15. A method for making a turbomachine part, comprising: machining a blank into a base having a first vane and a second vane extending therefrom, the first vane and the second vane defining a channel therebetween; filling the channel with a refractory material to form a bridge between a first top of the first vane and a second top of the second vane; curing the refractory material; preheating the first vane and the second vane to a preheating temperature below a melting temperature thereof; and forming a cover on the first top and the second top and over the bridge with a molten metal, the cover being formed such that the base, the first vane, the second vane, and the cover form a substantially homogenous structure.
 16. The method of claim 15, wherein machining the blank comprises flaring a first bottom of the first vane and a second bottom of the second vane.
 17. The method of claim 15, wherein machining the blank comprises flaring the first top of the first vane and the second top of the second vane.
 18. The method of claim 15, wherein forming the cover comprises: disposing a dam around an outside diameter of the base such that the dam, the first top of the first vane, the second top of the second vane, and the bridge define a bounded region; and pouring the molten metal into the bounded region to melt a portion of the first top and a portion of the second top.
 19. The method of claim 18, wherein forming the cover further comprises controlling the preheating temperature and a temperature of the molten metal to form the substantially homogenous structure.
 20. The method of claim 19, wherein forming the cover further comprises controlling the preheating temperature and a temperature of the molten metal to prevent oxidation of the first vane, the second vane, and the cover. 